Bacterial Spoilage and its Prevention in Packed Dairy Products

In the present research, five different locations were selected for the collection of dairy product samples. Five different bacteria were isolated and the identified bacterial isolates were Listeria sp., Yersinia sp., Campylobacter sp., Staphylococcus sp. and Pseudomonas sp. The species level identification of the five bacterial isolates were subjected to Phylogenetic analysis (16S rRNA Sequencing). The Listeria sp. was identified as Listeria monocytogenes, Yersinia sp. was Yersinia enterocolitica, Campylobacter sp. was identified as Campylobacter jejuni, Staphylococcus sp. was Staphylococcus aureus and Pseudomonas sp. was identified as Pseudomonas fluorescens. The effects of different concentrations of organic acids (Acetic acid, Lactic acid and Sorbic acid) and chemical preservatives (Potassium sorbate, Sodium nitrate and Sodium propionate) on the growth of the dairy product spoilage bacterial strains were studied. Highest zone of inhibition was recorded against Listeria monocytogenes, Staphylococcus aureus, Yersinia enterocolitica and Pseudomonas aeruginosa. The effect of culture filtrate and crude bacteriocin of Lactobacillus lactis and Lactobacillus acidophilus on the inhibition of growth of five dairy spoilage bacterial strains was studied. The diameter of the inhibition zone of all the bacterial strains was increased with increase in concentration of culture filtrate from 20 to 100 µg ml-1. Highest zone of inhibition was observed against Listeria monocytogenes, Staphylococcus aureus, Yersinia enterocolitica and Pseudomonas aeruginosa. Lowest zone of inhibition was recorded in Campylobacter jejuni. The Minimum inhibitory concentration (MIC) of crude bacteriocin of Lactobacillus lactis against all the dairy spoilage bacterial strains was assessed. The Campylobacter jejuni recorded lower MIC (50 µl) followed by Pseudomonas aeruginosa (60 µl), Yersinia enterocolitica (70 µl), Staphylococcus aureus (80 µl) and Listeria monocytogenes (90 µl) was inhibited. The inhibitory effect of heat stability of crude bacteriocin (extracted from Lactobacillus lactis and Lactobacillus acidophilus) at various time intervals and different temperatures against dairy product spoilage bacteria were studied. The inhibitory activity was unaffected by heating upto 120 °C for 40 min and 70 % of activity retained after heat treatment at 120 °C for 15 min. More inhibition was noted in 15 min time interval at 20 °C followed by 40 °C, 60 °C, 80 °C, 100 °C and 120 °C. The inhibitory effect of surfactant on stability of crude bacteriocin Lactobacillus lactis and Lactobacillus acidophilus against dairy product spoilage bacteria was studied. Among the various surfactants at various concentrations of 0.2, 0.4, 0.6, 0.8 and 1.0 per cent, HDTMEB exhibited more inhibitory activity against dairy product spoilage bacteria followed by SDS, EDTA, TWEEN 80 and TWEEN 20. The inhibitory effect of metal ion on crude bacteriocin on Lactobacillus lactis and Lactobacillus acidophilus against dairy product spoilage bacteria was studied at various concentrations viz., 5 mg/L, 10 mg/L, 15 mg/L, 20 mg/L and 25 mg/L. It was observed that the inhibition zone diameter was decreased while the concentration of the metal ion was increased. Of the various metal ion tested, Copper sulphate showed maximum inhibitory effect against Listeria monocytogenes at 5 mg/L concentration followed by Ferrous sulphate, Calcium chloride, Zinc sulphate and Mercuric chloride.